BILATERAL DIFFERENCES IN NORMALISED TRICEPS

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BILATERAL DIFFERENCES IN NORMALISED TRICEPS
SURAE ELECTROMYOGRAMS AND GROUND REAC- TION
FORCES DURING A PLYOMETRIC TASK Ball Nick, Scurr
Joanna, Wood Louise (University of Portsmouth,
United Kingdom) The plyometric bounce drop jump
focuses on plantar flexor muscle development,
which is activated prior to contact to stiffen
the joint, prevent joint collapse upon contact
and perform an efficient push off phase (Bobbert
et al, 1987 Dyhre-Poulsen et al, 1991).
Bilateral neuromuscular com-parison is required
due to the tendency to touch the feet down at
different times potentially causing preferential
overloading of one limb. This study aims to
compare the neuromuscular contribution between
left and right triceps surae in the pre-,
initial- and post-contact phases of a bi-lateral
drop jump exercise to assess the consequences of
non-simultaneous foot placement. Following
ethical approval, 16 male participants (age 25
4.7 yr height 1.790.05 m body mass 76.98.5
kg) performed 1 set of drop jumps from 0.4m.
Electromyo-graphy (EMG) activity of the soleus,
medial gastrocnemius and lateral gastrocnemius of
both legs was recorded us-ing active bipolar
pre-amplified disc electrodes (Biomet-rics, UK)
(gain x 1000 input impedance gt10k937 CMRR
gt96dB bandpass, 10-1000Hz noise lt5uV). The EMG
sig-nals were amplified (1000v) and sampled at
1000 Hz. The electrodes were attached to a
Biometrics DataLog EMG system. Two Kistler force
platforms (0.6 x 0.4m, natural frequency 1000 Hz)
were used to measure the resultant ground
reaction force (GRF), ground contact time and
du-ration of the drop jumps. Peak RMS EMG
amplitudes were recorded from each phase of the
drop jump. The EMG data was normalised to a
reference dynamic muscle action (20m sprint).
Repeated measures ANOVA compared bilat-eral EMG
activity, resultant peak GRFs and contact
dura-tions. Pearsons correlations (r)
ascertained relationships between normalised EMG
activity and contact time. Post-contact phase
EMG showed sub-maximal triceps surae activation.
No differences between the muscles within and
between each leg (pgt0.05) were shown.
Dif-ferences were evident in pre- and
post-contact normalised EMG activity (plt0.01) and
initial- and post-contact EMG (plt0.05). A
significant relationship was found between peak
resultant GRF and contact duration for both left
(r 0.65) and right leg (r 0.66). A weak
relationship was found between peak resultant GRF
and non-simultaneous foot contact (r 0.5).
Minimal time differential between bi-lateral foot
contacts showed no relationship to EMG activ-ity.
This study showed minimal differences between
left and right triceps surae neuromuscular
strategies engaged dur-ing a drop jump task.
Differences in contact time initiation were
present, however are not significant enough to
cause neuromuscular differences in the plantar
flexor muscles. Bobbert, M.F et al (1987) Drop
Jumping II. The influence of dropping height on
the biomechanics of drop jumping. Med Sci Sport
Ex, 19, 339-346 Dyhre-Poulsen, P. et al (1991)
Dynamic control of muscle
stiffness and H reflex modulation during hopping
and jump-ing in man. J Physy 437, 287-304.
Keywords Jumping, Electromyography, Strength
and Con-ditioning
12thAnnual Congress of the ECSS, 1114 July 2007,
Jyväskylä, Finland I